US4870533A - Transistor protection circuit - Google Patents

Transistor protection circuit Download PDF

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Publication number
US4870533A
US4870533A US07/102,308 US10230887A US4870533A US 4870533 A US4870533 A US 4870533A US 10230887 A US10230887 A US 10230887A US 4870533 A US4870533 A US 4870533A
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Prior art keywords
transistor
current
collector
emitter
base
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US07/102,308
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English (en)
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Johannes P. M. Bahlmann
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US Philips Corp
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US Philips Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/52—Circuit arrangements for protecting such amplifiers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S323/00—Electricity: power supply or regulation systems
    • Y10S323/907—Temperature compensation of semiconductor

Definitions

  • This invention relates to a transistor protection circuit comprising:
  • an output transistor of a first conductivity type comprising a collector, base and emitter
  • a driver transistor of the first conductivity type comprising a collector, base and emitter, the emitter being coupled to the base of the output transistor
  • a current-sensing transistor of the first conductivity type comprising a collector, base and emitter, having its base and emitter coupled to the base and the emitter, respectively, of the output transistor, its collector current being a measure of the collector current of the output transistor, and
  • Such a circuit may be used, for example, in audio and video circuitry and in motor-control circuits.
  • Such a circuit is known from inter alia, U.S. Pat. No. 4,330,757.
  • the current through the output transistor is measured by means of a current-sensing transistor whose base-emitter junction is arranged in parallel with that of the output transistor, the collector current of the current-sensing transistor being a fraction of the collector current of the output transistor.
  • a current mirror the collector current of the current-sensing transistor is reflected to a resistance element which is arranged in parallel with the base-emitter junction of a clamping transistor, the collector of the clamping transistor being connected to the base of the driver transistor.
  • the clamping transistor is driven into conduction so that, what would otherwise be a part of the base current of the driver transistor is drained via the clamping transistor.
  • a disadvantage of this known circuit arrangement is that in integrated form it exhibits a high degree of instability in the protection loop. These instabilities are caused by phase shifts in the current mirror arranged in the protection loop, which current mirror comprises PNP-transistors which have a comparatively low cut-off frequency.
  • a transistor protection circuit which has a stable protection loop and which is suitable for manufacture in integrated form.
  • a transistor protection circuit of the type specified in the opening paragraph is characterized in that the current limiting means are provided with:
  • a current generator for supplying a reference current, the generator output being coupled to the collector of the current-sensing transistor, and
  • the invention utilizes the principle that in the event that the collector current of the current-sensing transistor becomes larger than the reference current from the current generator, the voltage at the output of the current generator changes from a high to a low value, thereby turning on a semiconductor junction by means of which the drive current to the output transistor is limited.
  • the protection loop exhibits no instabilities because the protection loop only comprises transistors of one conductivity-type. Moreover, the arrangement is highly suitable for fabrication as an integrated circuit.
  • the semiconductor P/N junction may be coupled to the output of the current generator via an emitter-follower transistor of the first conductivity type comprising a collector, base, and emitter, which follower transistor has its base coupled to the output of the current generator and its emitter coupled to the semiconductor junction.
  • the semiconductor junction may comprise the collector-base junction of the driver transistor, the collector of the driver transistor being coupled to the emitter of the follower transistor.
  • the protection circuit is actuated the driver transistor is bottomed, thereby limiting the base current of the output transistor.
  • the semiconductor junction may comprise a diode, or a transistor connected as a diode, having its cathode coupled to the emitter of the follower transistor and its anode coupled to the base of the driver transistor.
  • the protection circuit becomes operative a part of what would otherwise be the base current of the driver transistor is drained via the diode so that the current through the output transistor is limited.
  • the cathode may be connected directly to the output of the current generator.
  • the current generator for supplying the reference current may comprise a constant current source or a reference resistor in series with a reference-voltage source.
  • a limiting resistor may be arranged in the collector line of the follower transistor.
  • FIG. 1 shows a first embodiment
  • FIG. 2 shows a first variant of the circuit shown in FIG. 1,
  • FIG. 3 shows a second variant of the circuit shown in FIG. 1,
  • FIG. 4 shows a third variant of the circuit shown in FIG. 1,
  • FIG. 5 shows another embodiment
  • FIG. 6 shows another embodiment.
  • FIG. 1 shows a first embodiment of the invention.
  • transistor T 1 is the output transistor to be protected. This transistor can supply a current I o to a load 3, represented in broken lines, via the collector terminal 2.
  • the emitter of transistor T 1 is connected to the negative power-supply terminal 4, which in the present example is connected to ground.
  • the transistor T 1 is driven by a driver transistor T 2 having an emitter connected to the base of transistor T 1 .
  • An input current I i is applied to the base of transistor T 2 .
  • the output current I o In order to prevent the output transistor T 1 from being damaged by an excessive current, the output current I o must be limited to a maximum value.
  • the protection circuit comprises a current-sensing transistor T 3 whose base-emitter junction is arranged in parallel with that of transistor T 1 .
  • the base-emitter area A 3 of transistor T 3 is smaller than the base-emitter area A 1 of transistor T 1 , so that the collector current of transistor T 3 is equal to a fraction A 3 /A 1 of the collector current of transistor T 1 .
  • the collector of transistor T 3 is coupled to the positive power-supply terminal 6 by means of a current generator 5 which supplies a reference current I ref .
  • the collector of transistor T 3 is connected to the base 7 of a follower transistor T 4 having an emitter connected to the collector of driver transistor T 2 and a collector connected to the positive power-supply terminal 6.
  • an output current I o will flow in transistor T 1 .
  • This current depends on the input current I i and on the current-gain factors of the transistors T 2 and T 1 .
  • the collector current of transistor T 3 is then equal to a fraction of the output current I o .
  • the collector current of T 3 is smaller than the reference current I ref from the current generator 5 the transistor T 3 presents a load to the current generator 5.
  • the voltage at the base 7 of transistor T 4 is comparatively high.
  • the voltage of the emitter of transistor T 4 follows the volume on the base 7 with a difference corresponding to one base-emitter junction voltage.
  • the collector of transistor T 1 is at such a voltage that transistor T 1 conducts normally.
  • the protection circuit is activated at the instant that the collector current of transistor T 3 exceeds the reference current I ref .
  • the current generator 5 then presents a load to transistor T 3 .
  • the voltage at the base 7 of transistor T 4 changes to a comparatively low value.
  • the voltage on the emitter of the transistor T 4 and hence on the collector of transistor T 2 then becomes so low that the base-collector junction of transistor T 2 , which is normally cut off, is forward-biased.
  • Transistor T 2 is then bottomed so that transistor T 2 practically ceases to function as a current amplifier.
  • the emitter current of transistor T 2 is then of the same order of magnitude as the input current I.sub. i.
  • Transistors T 1 and T 4 have current-gain factors ⁇ which in practice are of the order of magnitude of 100.
  • I omax 500 mA
  • the maximum collector-emitter current of the transistors T 2 and T 4 may be approximately 5 mA, so that the base current of transistor T 4 will be approximately 1/20 mA.
  • a 1 /A 3 between the emitter areas ⁇ 500 the collector current of transistor T 3 will be substantially 1 mA, which is large relative to the base current of transistor T 4 .
  • this ratio may be adjusted by arranging a resistor in the emitter line of one of the transistors T 1 and T 3 or by arranging a resistor in both emitter lines.
  • the ratio I omax /I ref becomes temperature-dependent unless the ratio between the resistor values is inversely proportional to the ratio between the emitter areas.
  • FIG. 2 shows a first variant of the circuit shown in FIG. 1, similar components bearing the same reference numerals.
  • the current generator 5 for supplying the reference current I ref comprises a current source.
  • This current source comprises a reference resistor 8 which, in series with a PNP-transistor T 5 arranged as a diode, is clamped between the negative and the positive power-supply terminals 4 and 6. If the resistance of the resistor 8 is sufficiently high the current in this branch is almost wholly determined by this resistor.
  • a transistor T 6 whose base-emitter path is connected in parallel with that of transistor T 5 , this current is reflected to the collector of transistor T 3 .
  • the present embodiment employs PNP-transistors T 5 and T 6 , but these transistors do not affect the stability of the circuit because they do not form part of the feedback loop comprising the transistors T 3 , T 4 and T 2 .
  • the circuit operates in the same way as that in FIG. 1. If the collector current of transistor T 3 is smaller than the collector current I ref of transistor T 6 , transistor T 3 with its high collector-impedance constitutes a load for the current source transistor T 6 and the voltage at point 7 is comparatively high. However, if the collector current of transistor T 3 is larger than the collector current I ref of transistor T 6 , transistor T 6 with its high collector impedance presents a load to the transistor T 3 , which then functions as the current-source transistor. The voltage at point 7 is then comparatively low so that transistor T 2 is bottomed.
  • the current generator in this variant comprises a reference resistor 9, of which one terminal is connected to the collector of transistor T 3 and the other terminal is connected to a reference voltage V ref .
  • the reference current I ref is substantially equal to the quotient of the reference voltage and the resistance value of the resistor 9 if the reference voltage is not too low and the resistance of said resistor is sufficiently high.
  • the circuit operates in the same way as that shown in FIGS. 1 and 2, the reference resistor forming a load for transistor T 3 when the protection circuit is activated so that the voltage on point 7 changes and transistor T 2 is bottomed.
  • the operation of the protection circuit and consequently the maximum output current I o , can be made substantially temperature-independent. More particularly, it can be arranged that a voltage with a positive temperature coefficient appears across the reference resistor, which coefficient is substantially equal to the positive temperature coefficient of the reference resistor, so that the reference current is substantially temperature-independent.
  • FIG. 4 A third variant of the circuit shown in FIG. 1 is shown in FIG. 4, in which similar components bear the same reference numerals.
  • the current generator in this variant comprises a reference resistor 9 to which a reference voltage V ref is applied.
  • V ref a reference voltage
  • the NPN-transistor T 1 gives rise to a parasitic PNP-transistor T 1 ', whose collector is connected to the substrate of the integrated circuit, whose base is connected to the collector of transistor T 1 and whose emitter is connected to the base of transistor T 1 .
  • This transistor T 1 ' is shown in broken lines in the Figure. When transistor T 1 is bottomed its collector voltage drops below its base voltage so that the base-emitter junction of the parasitic transistor T 1 ' is driven into conduction.
  • the drive current of transistor T 1 which is supplied by transistor T 2 , may than become fairly large, which demands an unnecessary amount of power.
  • a limiting resistor 10 is arranged in the collector line of transistor T 4 , which limiting resistor is coupled to the positive power-supply terminal 6 via a transistor T 7 whose base is at the reference voltage V ref . It is to be noted that as an alternative the limiting resistor may be connected directly to the positive power-supply terminal 6.
  • FIG. 5 Another protection circuit in accordance with the invention will be described with reference to FIG. 5 in which idential parts bear the same reference numerals as in FIG. 1.
  • the emitter of transistor T 4 is no longer connected to the collector of transistor T 2 , but T 4 is still arranged as an emitter-follower, the current source 12 being arranged in its emitter line.
  • the cathode of a diode 13 is connected to the emitter of transistor T 4 , the anode of said diode being connected to the base of transistor T 2 .
  • a diode it is possible to employ a transistor with a short-circuited base-collector junction.
  • FIG. 6 Another transistor protection circuit in accordance with the invention will be described with reference to FIG. 6, in which idential parts bear the same reference numerals as in FIG. 5.
  • the cathode of the diode 13 is now connected directly to the output 7 of the current generator 5 instead of via a follower transistor.
  • the circuit operates in the same way as that shown in FIG. 5.
  • the protection circuit When the protection circuit is activated a part of what would otherwise be the base current of transistor T 2 flows through the collector of transistor T 3 via diode 13. This current is small relative to the reference current I ref so that its influence on the maximum value of the output current of transistor T 1 may be ignored.
  • the invention is not limited to the embodiments described but many variations are possible within the scope of the invention as defined by the claims.
  • the current generator may be constructed in various ways.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
US07/102,308 1983-08-18 1987-09-25 Transistor protection circuit Expired - Lifetime US4870533A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NL8302902 1983-08-18
NL8302902A NL8302902A (nl) 1983-08-18 1983-08-18 Transistorbeveiligingsschakeling.

Related Parent Applications (1)

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US06636034 Continuation 1984-07-30

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US4870533A true US4870533A (en) 1989-09-26

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US07/102,308 Expired - Lifetime US4870533A (en) 1983-08-18 1987-09-25 Transistor protection circuit

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US (1) US4870533A (nl)
EP (1) EP0142177B1 (nl)
JP (1) JPS6059807A (nl)
CA (1) CA1228129A (nl)
DE (1) DE3470638D1 (nl)
HK (1) HK84191A (nl)
NL (1) NL8302902A (nl)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5343141A (en) * 1992-06-09 1994-08-30 Cherry Semiconductor Corporation Transistor overcurrent protection circuit
US5428287A (en) * 1992-06-16 1995-06-27 Cherry Semiconductor Corporation Thermally matched current limit circuit
US5721512A (en) * 1996-04-23 1998-02-24 Analog Devices, Inc. Current mirror with input voltage set by saturated collector-emitter voltage
WO2001047104A1 (en) * 1999-12-22 2001-06-28 Micro Analog Systems Oy Emitter follower with constant collector current biasing means
US20020024390A1 (en) * 2000-08-31 2002-02-28 Hitachi, Ltd. Power amplifier module
GB2372894A (en) * 2000-12-07 2002-09-04 Eugueni Sergeyevich Alechine Method for thermal stabilisation of operating conditions in transistors
US20040232968A1 (en) * 2003-05-19 2004-11-25 Analog Devices, Inc. Dynamic method for limiting the reverse base-emitter voltage

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS62225012A (ja) * 1986-03-27 1987-10-03 Matsushita Electric Ind Co Ltd プツシユプル増幅器
JPH0744397B2 (ja) * 1986-03-27 1995-05-15 松下電器産業株式会社 プツシユプル増幅器
JPS62225011A (ja) * 1986-03-27 1987-10-03 Matsushita Electric Ind Co Ltd プツシユプル増幅器
JP2790496B2 (ja) * 1989-11-10 1998-08-27 富士通株式会社 増幅回路
US5383083A (en) * 1992-05-19 1995-01-17 Pioneer Electronic Corporation Protective apparatus for power transistor
FR2762726B1 (fr) * 1997-04-29 2000-02-25 Sgs Thomson Microelectronics Etage de sortie d'amplificateur a protection contre les courts-circuits

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3792316A (en) * 1972-05-15 1974-02-12 Soc Gen Semiconduttori Spa Protection device for a power element of an integrated circuit
US3845405A (en) * 1973-05-24 1974-10-29 Rca Corp Composite transistor device with over current protection
US3924158A (en) * 1974-10-24 1975-12-02 Hughes Aircraft Co Electronic overload protection device
US4021701A (en) * 1975-12-08 1977-05-03 Motorola, Inc. Transistor protection circuit
US4321648A (en) * 1981-02-25 1982-03-23 Rca Corporation Over-current protection circuits for power transistors
US4330757A (en) * 1977-12-09 1982-05-18 Nippon Electric Co., Ltd. Semiconductor power amplification circuit

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1323640A (en) * 1972-06-22 1973-07-18 Standard Telephones Cables Ltd Circuit incorporating current limiting arrangement
DE2507741C3 (de) * 1975-02-22 1979-05-17 Deutsche Itt Industries Gmbh, 7800 Freiburg Überstromgeschützte, universell verwendbare Transistoranordnung
US4078207A (en) * 1977-01-07 1978-03-07 Rca Corporation Push-pull transistor amplifier with driver circuitry providing over-current protection
DE2705583C2 (de) * 1977-02-10 1982-04-08 Siemens AG, 1000 Berlin und 8000 München Transistorschaltung mit einem vor thermischer Zerstörung zu schützenden Transistor
JPS55128908A (en) * 1979-03-27 1980-10-06 Toshiba Corp Transistor protective circuit

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3792316A (en) * 1972-05-15 1974-02-12 Soc Gen Semiconduttori Spa Protection device for a power element of an integrated circuit
US3845405A (en) * 1973-05-24 1974-10-29 Rca Corp Composite transistor device with over current protection
US3924158A (en) * 1974-10-24 1975-12-02 Hughes Aircraft Co Electronic overload protection device
US4021701A (en) * 1975-12-08 1977-05-03 Motorola, Inc. Transistor protection circuit
US4330757A (en) * 1977-12-09 1982-05-18 Nippon Electric Co., Ltd. Semiconductor power amplification circuit
US4321648A (en) * 1981-02-25 1982-03-23 Rca Corporation Over-current protection circuits for power transistors

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5343141A (en) * 1992-06-09 1994-08-30 Cherry Semiconductor Corporation Transistor overcurrent protection circuit
US5428287A (en) * 1992-06-16 1995-06-27 Cherry Semiconductor Corporation Thermally matched current limit circuit
US5721512A (en) * 1996-04-23 1998-02-24 Analog Devices, Inc. Current mirror with input voltage set by saturated collector-emitter voltage
WO2001047104A1 (en) * 1999-12-22 2001-06-28 Micro Analog Systems Oy Emitter follower with constant collector current biasing means
US20020024390A1 (en) * 2000-08-31 2002-02-28 Hitachi, Ltd. Power amplifier module
US6816017B2 (en) * 2000-08-31 2004-11-09 Renesas Technology Corp. Power amplifier module
GB2372894A (en) * 2000-12-07 2002-09-04 Eugueni Sergeyevich Alechine Method for thermal stabilisation of operating conditions in transistors
GB2372894B (en) * 2000-12-07 2003-07-30 Eugueni Sergeyevich Alechine Method for thermal stabilisation of operating conditions in transistorised electronic devices
US20040232968A1 (en) * 2003-05-19 2004-11-25 Analog Devices, Inc. Dynamic method for limiting the reverse base-emitter voltage
US6844768B2 (en) 2003-05-19 2005-01-18 Analog Devices, Inc. Dynamic method for limiting the reverse base-emitter voltage

Also Published As

Publication number Publication date
CA1228129A (en) 1987-10-13
NL8302902A (nl) 1985-03-18
DE3470638D1 (en) 1988-05-26
EP0142177B1 (en) 1988-04-20
EP0142177A1 (en) 1985-05-22
JPH0516689B2 (nl) 1993-03-05
JPS6059807A (ja) 1985-04-06
HK84191A (en) 1991-11-01

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